This application claims the priority of British patent document 9821320.0, filed Oct. 1, 1998, the disclosure of which is expressly incorporated by reference herein.
This invention relates to sensor systems and more particular relates to acoustic sensor systems for naval applications.
Land based acoustic sensor systems for locating the position of guns for example, or other noise generators invisible to radar, by detection and analysis of the sound produced, are well known. However, a problem arises when attempting to use this technology for naval applications, since ships carrying the necessary equipment for identifying the location and classification of noise generating targets on or over land, must, in order for the equipment to be operationally effective, approach to within relatively close range of the noise source, whereby they become more vulnerable to attack. The early detection and location by surface vessels in littoral (coastal) waters, of missile-carrying hovering helicopters, which may briefly rise above vegetation or other coastal cover in order to launch a low level attack, is particularly desirable, given the vulnerability to such helicopters.
It is an object of this invention to provide an acoustic sensor system for naval use, which facilitates the detection, location and classification from ships, of noise-generating targets over land, wherein the aforementioned problem is largely overcome, or at least acceptably reduced.
According to the present invention an acoustic sensor system for the detection, location and classification of sound-generating targets from a ship comprises a base station aboard the ship which includes a radio transmitter/receiver (B-Tx/Rx) and a digital signal processor unit (DSP); and a plurality of floating remote stations which in use are positioned remotely from the ship, and which are each arranged to carry apparatus including an electrical power source, a radio transmitter/receiver (STx/Rx) suitable for two way communication with the B-Tx/Rx, control means, sound detector means, and a data processor (DP), the control means being responsive to signals transmitted from the B-Tx/Rx and received by the S-Tx/Rx for controlling provision of electrical power for the apparatus and the DP being operative to classify electrical signals generated by the sound detector means in response to the reception thereby of sound signals and operative to initiate in dependence upon classification, transmission of data from the S-Tx/Rx to the B-Tx/Rx appertaining to the sound signals, the DSP being operative in dependence upon reception of these signals from each of the remote stations, to generate data derived therefrom appertaining to the position and classification of the sound source.
The floating remote stations may be buoys which may be placed covertly by a small craft operating from the ship for example, or alternatively they may be small unmanned power driven boats, which will hereinafter be referred to as unmanned surface vessels or USVs, operated remotely under control of personnel aboard the ship and positionally controlled in dependence upon signals from the DSP at the base station which are fed via the control means at the remote station.
It will be appreciated that by deploying sound sensors which are positioned well away from the ship but in communication therewith, the advantages of location using acoustic sensor technology may be enjoyed without suffering the drawback of ship-mounting. Mounting microphones on a ship leads to two problems: (i) they will be a considerable distance from the target (say 5 km or more), and (ii) the local noise from the ship will significantly desensitise them, even after the application of noise reduction techniques. The many sources of reciprocating/rotating machinery on a ship will constitute a complex sound field, which Will be very difficult to reduce, automatically or manually.
The DP may comprise a simple threshold detector responsive only to signals above a predetermined threshold, this simple classification of received sound signals being enhanced by further processing in the DSP for target identification as well as target location i.e. determination of target bearing and range.
Alternatively, the DP may be arranged to carry out more sophisticated processing for many, or all aspects of target identification and location, as determined in accordance with the particular application in view. It may be desirable to enhance the capability of the DP so that signals in certain frequency bands or with other characteristics are either accepted or rejected at this early stage in the processing. This will enable some degree of data reduction before transmission back to the ship. It will however be apparent that since a plurality of remote stations are involved, in most cases it may be most appropriate to do the majority of the required processing at the base station.
The sound detector means may comprise at least one microphone sensor responsive to airborne sounds.
Additionally, an underwater sensor or sensors may be provided responsive to corresponding waterborne sounds the output of which may be used in combination with signals derived from the microphone sensor. The microphone sensor may comprise a single sensor.
Alternatively it may comprise an array having several microphone each of which may be supported on a boom or booms.
The remote stations may be provided with sensors responsive to radiation other than sound, i.e. infra-red radiation, the character of which may be analyzed and used as an additional information source or to supplement data derived from the sound sensor means.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.